1. Field of the Invention
The present invention relates to a linear amplifier for amplifying power of a radio-frequency signal whose level varies widely, based on feed-forward technique.
2. Description of the Related Art
In recent years, a CDMA (Code Division Multiple Access) has been applied to many mobile communication systems since it has characteristics that it has a high ability of keeping confidentiality and is not easily influenced by selective fading and other interference/jamming in a radio transmission path and also since technology of realizing transmitting power control which is indispensable for solving a near-far problem which is peculiar to it has been established.
Wireless zones of these mobile communication systems are formed, via redundantly structured power amplifiers and directional antennas, as a plurality of sector cells having the following advantages.
to be able to reduce interferences of the same channel and improve utilization efficiency of radio frequencies based on directivity of the antennas
to be able to have a large number of co-callers (number of subscribers) per unit frequency compared with that in omni-zones
to be able to perform channel control (including transmitting power control) independently for each sector
Feed-forward technique is also applied to many of the power amplifiers described above.
FIG. 16 is a diagram showing a structure example of the power amplifier to which the feed-forward technique is applied.
In the drawing, an input of a variable attenuator 41 is given an input signal whose power is to be amplified (hereinafter referred to as a xe2x80x98principal signalxe2x80x99) and an output of the variable attenuator 41 is connected to inputs of a variable attenuator 42 and a delaying part 43. An output of the variable attenuator 42 is connected to an input of a main amplifier 45 via a variable phase-shifter 44 and an output of the main amplifier 45 is connected to an input of the attenuator 46. Outputs of the delaying part 43 and the attenuator 46 are connected to an input of a variable attenuator 47 and an output of the variable attenuator 47, as well as the output of the main amplifier 45, is connected to an input of a pilot signal detecting part 51 via a variable phase-shifter 48, an auxiliary amplifier 49, and a detector 50. To the input of the variable attenuator 42, an output of a pilot signal generating part 52 is connected via a variable attenuator 53 and to control inputs of the variable attenuators 41, 42, 47 and the variable phase-shifters 44, 48 as well as control inputs of the pilot signal generating part 52 and the variable attenuator 53, corresponding output ports of a controlling part 54 are connected. Monitor outputs of the detector 50 and the pilot signal detecting part 51 are connected to corresponding input ports of the controlling part 54 and in an output of the pilot signal detecting part 51, the principal signal to be transmitted as a transmission wave is obtained.
Note that a loop-shaped circuit which is formed between the output of the variable attenuator 41 and the input of the variable attenuator 47 is hereinafter referred to as an xe2x80x98error detection loopxe2x80x99 (a principal-signal cancellation loop) and a loop-shaped circuit which is formed between the output of the main amplifier 45 and the input of the pilot signal detecting part 51 is referred to as an xe2x80x98error elimination loopxe2x80x99 (a distortion cancellation loop).
Operations of the power amplifier as structured above in its steady state are explained below.
The variable attenuator 41 is given by the controlling part 54 attenuation which is determined under the channel control (may include the transmitting power control) and applies to each of the variable attenuator 42 and the delaying part 43 the principal signal at a level at which predetermined transmitting power is achieved.
The pilot signal generating part 52 constantly generates a sine wave signal (hereinafter referred to as a xe2x80x98pilot signalxe2x80x99) with a known frequency outside an occupied bandwidth of the principal signal and applies the pilot signal at a predetermined level to the input of the variable attenuator 42 via the variable attenuator 53 whose attenuation is set by the controlling part 54.
The main amplifier 45 gives to the attenuator 46 a signal obtained by amplifying the principal signal and the pilot signal which are applied via the variable attenuator 42 and the variable phase-shifter 44 (hereinafter referred to as a xe2x80x98provisional output-signalxe2x80x99). The attenuator 46 has attenuation equal to an inverse number of a nominal value of a total gain of the variable attenuator 42, the variable attenuator 44, and the main amplifier 45 which are cascaded and generates a signal corresponding to the sum of the principal signal inputted to the variable attenuator 42 and the pilot signal (hereinafter referred to as a xe2x80x98reduced input-signalxe2x80x99).
Delay time of the delaying part 43 is set in advance at a value equal to a sum (difference) of a nominal value of total propagation delay time of the variable attenuator 42, the variable phase-shifter 44, the main amplifier 45, and the attenuator 46 which are cascaded and time corresponding to a half of a cycle of the principal signal.
The delaying part 43 delays the principal signal outputted by the variable attenuator 41 over this delay time to output a signal whose phase is 180 degrees ahead of (delayed behind) the reduced input-signal which is obtained in the output of the attenuator 46 (hereinafter referred to as a xe2x80x98principal-signal cancellation signalxe2x80x99).
The variable attenuator 47, the variable phase-shifter 48, the auxiliary amplifier 49, and the detector 50 vary a level and a phase of a signal which is given as a sum string of instantaneous values of the reduced input-signal and the principal-signal cancellation signal under control of the controlling part 54 to generate a xe2x80x98distortion cancellation signalxe2x80x99.
The detector 50 extracts and detects a component of the principal signal included in the distortion cancellation signal to detect a level of the component of the principal signal.
Furthermore, the pilot signal detecting part 51 outputs a signal which is given as a sum of the provisional output-signal and the distortion cancellation signal and detects a level of a component of the pilot signal included in the signal.
Meanwhile, the controlling part 54 sets at a starting time a level of the pilot signal which is applied to the variable attenuator 42 by setting the aforesaid attenuation for the variable attenuator 53 (FIG. 17(1)) and supplies driving power to the main amplifier 45 via a power controlling part which is not shown (FIG. 17(2)).
The controlling part 54 also performs processing (hereinafter referred to as xe2x80x98initialization processingxe2x80x99) of setting attenuation ATTed, ATTes of the variable attenuators 42, 47 and phase-shift "PHgr"ed, "PHgr"es of the variable phase-shifters 44, 48 at predetermined initial values (here to simplify the explanation, supposed to be a digital value X (a positive pure binary number) at which the attenuation/the phase-shift become a mean value) (FIG. 17(3)).
After finishing the initialization processing, the controlling part 54 updates the attenuation ATTes of the variable attenuator 47 and the phase-shift "PHgr"es of the variable phase-shifter 48 at a predetermined frequency based on an adaptive algorithm for minimizing the level of the pilot signal which is detected by the pilot signal detecting part 51 (FIG. 17(4)). Note that processing of updating the attenuation ATTes of the variable attenuator 47 and the phase-shift "PHgr"es of the variable phase-shifter 48 in this way is hereinafter referred to simply as xe2x80x98distortion cancellation processingxe2x80x99.
Furthermore, after finishing the distortion cancellation processing, the controlling part 54 discriminates whether or not the level of the principal signal detected by a principal-signal detecting part (not shown) which is provided as a part of the pilot signal detecting part 51 exceeds a predetermined lower limit value (FIG. 17(5)) and as long as the result of the discrimination is false, it repeats the distortion cancellation processing without performing xe2x80x98principal-signal cancellation processingxe2x80x99 which is described later.
However, when the result of the discrimination is true, the controlling part 54 performs, in addition to the distortion cancellation processing, processing of updating the attenuation ATTed of the variable attenuator 42 and the phase-shift "PHgr"ed of the variable phase-shifter 44 (hereinafter referred to as xe2x80x98principal-signal cancellation processingxe2x80x99) based on an adaptive algorithm for minimizing the level of the principal signal detected by the detector 50 (FIG. 17(6)).
Therefore, since components of the principal signals included in the reduced input-signal and the principal-signal cancellation signal are maintained in a state in which their amplitude is equal to each other and their phases are different by 180 degrees from each other, the variable attenuator 47 is fed the following components included in the reduced input-signal.
the component of the pilot signal
a component of distortion which is generated by the main amplifier 45 according to the principal signal
Furthermore, since the following components included in the provisional output-signal and the distortion cancellation signal are maintained in a state in which their amplitude is equal to each other and their phases are different by 180 degrees from each other, the input of the pilot signal detecting part 51 is fed the principal signal in which the component of the distortion generated by the main amplifier 45 is suppressed.
the component of the pilot signal
the component of the distortion which is generated by the main amplifier 45 according to the principal signal
Therefore, even when the attenuation set for the variable attenuator 41 by the controlling part 54 varies widely, the principal signal at a predetermined level consistent with the attenuation is obtained as a transmission wave without having a spurious.
Incidentally, in the conventional example described above, an amplitude characteristic and a phase characteristic of the power amplifier may possibly change depending not only on the structure of a circuit of the power amplifier but also on conditions (power of signals and environments) under which the power amplifier is in actual operation. Moreover, the amplitude characteristic and the phase characteristic may possibly shift or fluctuate in actual operational processes even when central values of the attenuation of the variable attenuators 42, 47 and the phase-shift of the variable phase-shifters 44, 48 are adjusted in advance to be optimum values when it is manufactured.
In the conventional example, in order to avoid occurrence of failures due to the shift and the fluctuation, the levels of the pilot signal and the principal signal are set at optimum values while sufficient time is taken to vary the attenuation of the variable attenuators 53, 41 in a perturbation process which is carried out at the starting time.
However, since there is a technical limit in shortening time required for the perturbation at the starting time, there is a high possibility that time required for substituting a standby system for an active system under a redundant structure, for example, in an n+1 stand-by system is not able to be shortened.
Furthermore, when the power amplifier is started at a high speed exceeding the limit in shortening the time required for the perturbation, the attenuation and the phase-shift which are set respectively for the variable attenuators and the variable phase-shifters may possibly have large deviations relative to the central values of the attenuation and phase-shift value ranges.
Therefore, in the perturbation process, the attenuation and the phase-shift are temporarily set at minimum values which are not the optimum values, and since a long time is taken for them to settle in the actual optimum values or they are maintained at the minimum values without settling in the optimum values, an excessively large level of distortion (the spurious) may possibly be generated.
Moreover, the pilot signal generating part 52 constantly generates the pilot signal irrespective of the attenuation of the variable attenuator 41 (the level of the inputted principal signal) so that even when the level of the principal signal inputted to the main amplifier 45 is low enough for a level of the distortion generated in the main amplifier 45 to be permissible, the component of the pilot signal is transmitted as the spurious and average power consumption is increased.
It is an object of the present invention to provide a linear amplifier which realizes cost reduction of a system and equipment to which it is applied and highly maintain their performance and reliability.
It is another object of the present invention to maintain linearity with high reliability immediately after it is started.
It is still another object of the present invention to achieve a high starting speed with high reliability and stably maintain the predetermined performance.
It is yet another object of the present invention to reduce running cost and enhance performance.
It is yet another object of the present invention to realize flexible adaptability to fluctuation in characteristics which may possibly occur due to changes in environmental conditions and aging and to highly maintain linearity.
It is yet another object of the present invention to realize flexible adaptability to fluctuation in characteristics and deviations and highly maintain linearity.
It is yet another object of the present invention to realize flexible adaptability to fluctuation in characteristics which may possibly occur due to changes in environmental conditions and aging and to highly maintain linearity.
It is yet another object of the present invention to highly maintain linearity while maintaining flexible adaptability to changes in environmental conditions.
It is yet another object of the present invention to stably and highly maintain linearity.
It is yet another object of the present invention to maintain stable performance.
It is yet another object of the present invention to realize flexible adaptability to equipment of various level diagrams.
It is yet another object of the present invention to enhance total reliability as well as realize cost reduction of equipment to which the above inventions are applied.
The above objects are achieved by a linear amplifier which is characterized in that appropriate transfer characteristics for an error elimination loop and an error detection loop are given in advance and the appropriate transfer characteristics are applied at a starting time.
In the linear amplifier as described above, time required for the error detection loop and the error elimination loop to shift to their steady states at the starting time is shortened.
The above objects are also achieved by a linear amplifier which is characterized in that appropriate transfer characteristics for an error elimination loop and an error detection loop are given in advance and the appropriate transfer characteristics are applied when a rate of change in a level of an inputted or an outputted principal signal exceeds a predetermined threshold.
In the linear amplifier as described above, even when the level of the principal signal increases/decreases abruptly, the error detection loop and the error elimination loop are capable of shifting promptly to their steady states which are appropriate for a new level of the principal signal.
The above objects are also achieved by a linear amplifier which is characterized in that initial values are determined as values at which a level of a pilot signal obtained in an output of the error detection loop becomes minimum, the initial values being initial values for each of a plurality of items whose cross-correlation is low and which gives transfer characteristics of an error detection loop, and the detecting done by scanning at a starting time while values of other items are fixed at predetermined values. The linear amplifier is also characterized in that an error elimination loop and a combination of the initial values are applied as appropriate transfer characteristics.
In the linear amplifier as described above, the transfer characteristics of the error detection loop and the error elimination loop are flexibly initialized at values consistent with actual characteristics at the starting time even when environmental conditions and a characteristic of each part may possibly change in a wide range.
The above objects are also achieved by a linear amplifier which is characterized in that injection of a pilot signal to an error detection loop is restricted during a period in which a level of a principal signal to be amplified is lower than a predetermined lower limit value.
In the linear amplifier as described above, when the level of the principal signal is low enough for a characteristic thereof to be considered to be linear, the pilot signal is prevented from being outputted as a spurious as well as power required for generating and superimposing the pilot signal is prevented from being consumed even when no support for discriminating the level is given by external equipment.
The above objects are also achieved by a linear amplifier which is characterized in that, according to a notice indicating a period in which a level of a principal signal to be amplified is lower than a predetermined lower limit value, injection of a pilot signal to an error detection loop is restricted during the period.
In the linear amplifier as described above, when the level of the principal signal is low enough for a characteristic thereof to be considered to be linear, the pilot signal is prevented from being outputted as a spurious as well as power required for generating and superimposing the pilot signal is prevented from being consumed as long as the level is surely recognized as the notice.
The above objects are also achieved by a linear amplifier which is characterized in that appropriate transfer characteristics which are actually set are recorded and reused.
In the linear amplifier as described above, transfer characteristics to be set for an error detection loop and an error elimination loop at a starting time or when a level of a principal signal changes abruptly are given as the actually appropriate transfer characteristics.
The above objects are also achieved by a linear amplifier which is characterized in that it comprises means for monitoring a level of a principal signal and means for storing transfer characteristics to be set for an error detection loop and an error elimination loop according to the level(s) of the principal signal, and the transfer characteristics corresponding to the level(s) of the actually monitored principal signal are applied as an appropriate transfer characteristic for the error detection loop and/or an appropriate transfer characteristic for the error elimination loop.
In the linear amplifier as described above, the transfer characteristics to be set for the error detection loop and the error elimination loop at a starting time or when the level of the principal signal changes abruptly are given as the transfer characteristics flexibly appropriate for the level even when linearity of an amplifying section varies according to the level of the principal signal.
The above objects are also achieved by a linear amplifier which is characterized in that appropriate transfer characteristics which are actually set are recorded according to a xe2x80x98monitored levelxe2x80x99 and they are reused.
In the linear amplifier as described above, transfer characteristics to be set for an error detection loop and an error elimination loop at a starting time or when a level of a principal signal changes abruptly are given as the actually appropriate transfer characteristics even when linearity varies according to the level of the principal signal.
The above objects are also achieved by a linear amplifier which is characterized in that it comprises means for monitoring a temperature and means in which transfer characteristics to be set for an error detection loop and an error elimination loop according to the monitored temperature are stored, and the transfer characteristics corresponding to the actually monitored temperature are applied as an appropriate transfer characteristic for the error detection loop and/or an appropriate transfer characteristic for the error elimination loop.
In the linear amplifier as described above, even when linearity varies according to the temperature as well as the level of the principal signal, the error detection loop and the error elimination loop are capable of maintaining their steady states with high reliability and stability while maintaining adaptability to deviations of the linearity.
The above objects are also achieved by a linear amplifier which is characterized in that appropriate transfer characteristics which are set for an error detection loop and an error elimination loop are recorded according to a xe2x80x98monitored temperaturexe2x80x99 and they are reused.
In the linear amplifier as described above, transfer characteristics to be set for the error detection loop and the error elimination loop at a starting time or when a level of a principal signal changes abruptly are given as the actually appropriate transfer characteristics even when linearity varies according to the temperature.
The above objects are also achieved by a linear amplifier which is characterized in that xe2x80x98appropriate transfer characteristicsxe2x80x99 are applied in place of new transfer characteristics to be updated, when deviations of the new transfer characteristics relative to xe2x80x98appropriate transfer characteristicsxe2x80x99 exceed predetermined upper limit values.
In the linear amplifier as described above, when an error detection loop and an error elimination loop deviate from or may possibly deviate from their steady states due to some cause under adaptive control, the transfer characteristics of the error detection loop and the error elimination loop are initialized to the appropriate transfer characteristics promptly.
The above objects are also achieved by a linear amplifier which is characterized in that it comprises means for setting a level of a principal signal at a low value at which xe2x80x98distortion occurring in an amplification elementxe2x80x99 is reduced, during a period in which each of the initial values of a plurality of items are obtained.
In the linear amplifier as described above, decrease in accuracy of the initial values which is caused because the amplification element operates in an excessively nonlinear region is prevented.
The above objects are also achieved by a linear amplifier which is characterized in that a level of a principal signal given from outside is set at a low value at which xe2x80x98distortion occurring in an amplification elementxe2x80x99 is reduced, during a period in which individual initial values of a plurality of items are obtained.
In the linear amplifier as described above, decrease in accuracy of the initial values which is caused because the amplification element operates in an excessively nonlinear region is prevented.
The above objects are also achieved by a linear amplifier which is characterized in that it comprises means for storing in advance correction values to be applied in correcting: a difference between levels of the principal signals amplified by the amplifying section, the difference which could occur between a level during the period in which the individual initial values of the plurality of items are obtained by the controlling section and a level after the period is over; and a margin between errors in the transfer characteristics of the error detection loop and the error elimination loop which occur individually according to the difference in the levels and a characteristic of the amplifying section. And, the initial values of the plurality of items according to an actual value of the difference in the levels are corrected, by using the correction values which are stored in the correction value storage section.
In the linear amplifier as described above, initial values of the transfer characteristics of the error detection loop and the error elimination loop are set at appropriate values with high reliability irrespective of the level of the principal signal after the period in which the individual initial values of the plural items are obtained by a controlling part is over.